American Medical Technologist (AMT) Practice Exam

What is the minimum volume required for a sputum specimen used for an acid-fast bacillus (AFB) test?

1. 1-2 mL

2. 3-5 mL

3. 5-10 mL

4. 10-15 mL

The correct answer is: 3-5 mL

The correct answer reflects the clinical standards for collecting sputum specimens specifically for acid-fast bacillus (AFB) testing, which is commonly used to diagnose tuberculosis. A volume of 3-5 mL of sputum is generally considered adequate to ensure that there is enough material for accurate microbial examination. This volume is significant because it provides enough sample to improve the sensitivity of the test, allowing for more reliable detection of the bacteria. When the amount of sputum is too small, it may not yield a sufficient quantity of organisms for a proper diagnosis, which can lead to false negatives and complicate patient management. For sputum specimens, laboratory protocols often emphasize that the sample should be obtained from a deep cough to improve the yield of respiratory pathogens. A sample within the suggested volume range helps facilitate adequate processing in the laboratory, ensuring that the diagnostic tests can be performed effectively. Volumes smaller than 3 mL may not be reliably diagnostic, while larger volumes, although potentially useful, are often unnecessary for the detection of AFB.